This subject matter disclosed herein relates generally to diagnostic imaging systems, and more particularly to detector collimation in Nuclear Medicine (NM) imaging systems.
In NM imaging, radiopharmaceuticals are taken internally and then detectors (e.g., gamma cameras), typically mounted on a gantry, capture and form images from the radiation emitted by the radiopharmaceuticals. The NM images primarily show physiological function of, for example, a patient or a portion of a patient being imaged.
In some types of scans, such as when scanning the whole body or with large patients, the portion of the patient being imaged may require the entire field of view of a conventional large size imaging detector. However, when imaging a structure that is smaller than the field of view of the imaging detector, such as the heart, liver, kidney, brain, breast or a tumor, portions of the imaging detector will acquire patient data outside of the structure of interest. Therefore, an effective sensitivity is decreased that is unrelated to collimator geometrical sensitivity, but results from the opportunity lost by not collecting useful information.
Collimation may be used to focus the field of view. In particular, a converging collimator can be used to improve the sensitivity of the detector over a limited field of view. For example, conventional converging fan beam collimators may be used wherein the lines of responses converge along a line. However, because the focal line is beyond the region of interest, the imaging volume decreases with decreasing distance to the focus such that objects of interest may be outside of the field of view and not imaged. Thus, multiple image scans may need to be performed or different types of collimators may be needed for different scans.